vte3: implement get/set rewrap_on_resize

Implement:
<setter>
Vte::Terminal#rewrap_on_resize= boolean
Vte::Terminal#set_rewrap_onresize(boolean)
<getter>
Vte::Terminal#rewrap_on_resize

```ruby
terminal = Vte::Terminal.new
terminal.rewrap_on_resize = true
p terminal.rewrap_on_resize #=> true
```

repoted by dark-yux. Thanks!!

fixes #257
vte3: add "?" to Vte::Terminal#rewrap_on_resize

Becuase this method is predicate.
vte3-gi: define constants under Terminal

e.g.
Vte::TerminalEraseBinding::DELETE_SEQUENCE is not rubyish.
Vte::Terminal::EraseBinding::DELETE_SEQUENCE is preferred in ruby.
vte3-gi test: modify test for `define constants under Terminal`
Revert "vte3-gi: define constants under Terminal"

This reverts commit 6ff9c5186d04ed9af0c774549c71a5e6138ba194.

It is for avoiding deep class tree.
ref: http://ruby-gnome2.sourceforge.jp/hiki.cgi?Naming+and+Conversion+Rules#Class%2FModule+names
Revert "vte3-gi test: modify test for `define constants under Terminal`"

This reverts commit 68ebd26985905bdef543245cd9a414b2ac51cb4d.

Avoiding deep class tree.
gtk2: use long instead of int

Because XChangeProperty(3) says:

> If the specified format is 8, the property data must be a char array.
>
> If the specified format is 16, the property data must be a short array.

> If the specified format is 32, the property data must be a long array.

In this case (format is 32 case), we should use a long array instead of
an int array.

GitHub: #256

Patch by mtasaka. Thanks!!!
gtk2: must use 8 for format when we use a character array

Because XChangeProperty(3) says:

> If the specified format is 8, the property data must be a char array.
gtk3: backport from gtk2

From XChangeProperty(3):

> If the specified format is 8, the property data must be a char array.
>
> If the specified format is 16, the property data must be a short array.
>
> If the specified format is 32, the property data must be a long array.
vte3: define constants where defined in Vte::Terminal

Constants where defined in Vte::Terminal are left as-is.
Because backward compatibility.
vte3: mark deprecated constants where in defined 'Vte::Terminal'
vte3: remove trailing space
vte3-gi: backport from vte3

mark deprecated constants where defined in `Vte::Terminal`
gi test: relax assertion in test_n_methods

In gobject-introspection-1.40.0, @info.n_methods returns 62.
But, in gobject-introspection-1.42.0, @info.n_methods returns 63.

`@info.n_methods` is expected to return vaule >=62.